igneous
Quartz-bearing feldspar pegmatite
Mostly quartz (SiO₂) and feldspar, likely with mica; a coarse granitic pegmatite
AI-generated identification · may be incorrectWhite to translucent quartz shows vitreous luster and hardness 7, while feldspar is typically hardness 6–6.5 with prominent cleavage. The very coarse, interlocking crystals and blocky cleavage are characteristic of pegmatite; exact mineral identification is limited by the image.
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Physical properties
White to translucent quartz shows vitreous luster and hardness 7, while feldspar is typically hardness 6–6.5 with prominent cleavage. The very coarse, interlocking crystals and blocky cleavage are characteristic of pegmatite; exact mineral identification is limited by the image.
Formation & geological history
Formed when water-rich granitic magma cooled slowly in veins or pockets, allowing unusually large crystals to grow, generally during Precambrian to Phanerozoic intrusive events. Pegmatites commonly crystallize late in a granite body.
Uses & applications
Used as a specimen for collecting; quartz and feldspar from pegmatites are important in glass, ceramics, electronics, and construction aggregate. Attractive transparent crystals may have modest decorative value.
Geological facts
The rounded white mass may be quartz, whereas the tan, angular material is likely feldspar with mica or iron staining. A glass-scratch test, cleavage inspection, and streak test can help distinguish the minerals.
Field identification & locations
Common in granite-associated pegmatite districts worldwide, including Brazil, the United States, Madagascar, and India. Typical rough specimens sell for about $5–$30; unusually large, clean, or gemmy crystals may bring $50–$200+.
